The Logic of Conceivability

Non-Categorical Thinking Workshop

Time: 09:45 - 17:30
Location: Amsterdam Science Park, ILLC, Room F1.15


The third workshop of the European Non-Categorical Thinking Project (EuNoC #3) will take place at the Institute for Logic, Language and Computation (ILLC) in Amsterdam. 




09.30-09.45: Coffee 


09.45-10.00: Welcome


10.00-10.50: Katrin Schulz (University of Amsterdam)


Title:  The similarity approach strikes back - negation in counterfactual conditionals


Abstract: In this talk I will reply to a recent challenge brought forward by Ciardelli et al. (2018) against the similarity approach to counterfactual conditionals. In this paper Ciardelli et al. argue that the natural language counterfactual doesn’t have a certain logical property that the similarity approach predicts. They take this to show that the approach in general fails and offer an alternative. I will put forward evidence showing that Ciardelli et al. (2018)’s solution doesn’t work. I will then continue arguing that the reason the solution doesn’t work is that the similarity approach is actually not the problem. The true culprit is the behaviour of negation in counterfactuals.


10.50-11.40: Arif Ahmed (University of Cambridge)


Title: Causal dependence and statistical evidence


Abstract: Many philosophers and legal theorists, going back at least as far as Thomson (1986), have proposed that an appeal to causal (or more generally, modal) connections is necessary for distinguishing statistical and 'individualized' evidence in cases where the difference seems to matter, for instance in legal cases involving evidence based on incidence rates vs. those involving eyewitness evidence. I argue that on the contrary there is a non-causal basis for making these discriminations. Accuracy, not causality, is what demands e.g. that we find against somebody who has been identified as guilty by an eyewitness with 80% reliability but not somebody that has been drawn from a population in which the incidence rate is 80%.


11.40-12.00: Coffee break


12.00-12.50: Shyane Siriwardena (University of Leeds)


Title: Counterfactuals and Indispensability in Williamson's Modal Epistemology


Abstract: The purpose of this talk will be to reconstruct the argument Williamson (2007) presents in Chapter 5 of The Philosophy of Philosophy. Williamson makes remarks that suggests he is interested in giving a naturalistic account of how we come to know things about metaphysical modality. However, the exact structure of his argument is somewhat unclear. Williamson gestures at the role of counterfactuals in ordinary reasoning, offers a sketch of our counterfactual epiistemology, and descrbies a logical relationship between modal propositions and counterfactual ones. I will make explicit the steps necessary to draw Williamson's desired conclusions from the topics at which he gestures.  

In the coures of the reconstruction, I will raise problems for Williamson's argument at several junctures. As Williamson's work has inspired a substantial body of work that broadly subscripes to his project (i.e. on that seeks to naturalise modal epistemology by way of subsuming it under the epistemology of counterfactuals), the current paper will show what work needs to be done for any Williamsonian account to be successful.



12.50-14.30: Lunch


14.30-15.20: Jan Sprenger (University of Turin)


Title:  Trivalent Semantics for Indicative Conditionals: A Resurrection Attempt


Abstract: The semantics of indicative conditionals are a notoriously difficult philosophical problem. Many philosophers take the view that they don't have classical truth conditions: the truth value of 'If A, then B', cannot be determined as a function of the truth values of A and B. Focus has therefore shifted to the acceptability and/or probability of indicative conditionals.

Unfortunately, this view severs the ties between the semantics and the epistemology of indicative conditionals. I propose a principled solution that goes back to De Finetti: to adopt a trivalent semantics, based on reading indicative conditionals as conditional predictions of the consequent. The talk explores advantages and drawbacks of this view.


15.20-16.10: Karolina Krzyzanowska (University of Amsterdam)


Title: Odd Conditionals


Abstract: It is a common intuition that the antecedent of an indicative conditional should be relevant for its consequent, that they should be somehow connected, yet only very few semantic theories of conditionals do justice to this intuition, while the majority tends to dismiss it as a pragmatic rather than a semantic phenomenon. However, no one has offered a satisfactory pragmatic explanation of why conditionals such as “If kangaroos have no gills, then they cannot fly” strike us as odd. In my talk, I will discuss some seemingly plausible pragmatic explanations of the oddity of missing-link conditionals and, drawing from the results of empirical studies on people's interpretation of indicative conditionals, I will show how they fail.


16.10-16.30: Coffee break


16.30-17.20: Paul Egré (Institut Jean-Nicod)


Title: Vagueness and moving thresholds


Abstract: According to Barker (2002), vague expressions can be used to update 
the context in relation to two kinds of uncertainty: uncertainty about
the standard of comparison operative in the conversational context
(what does "tall" mean around here?), and uncertainty about the
stimulus described ("is John tall?"). Lassiter (2011) and Lassiter and
Goodman (2015) have proposed a probabilistic account of vagueness
focusing mostly on the first kind of uncertainty. Other probabilistic
accounts of vagueness on the other hand (including Verheyen et al.
2010, Egré 2017) focus mostly on the second kind of uncertainty,
namely on the idea that categorization decisions are made relative to
a fixed threshold, but with various probabilities. In Egré (2017),
probabilities are introduced in relation to the idea that
categorization is a process of noisy magnitude estimation. In the IRT
models used by Verheyen et al. (2010), probabilities are supposed to
be a function of the item's similarity to a given anchoring value, but
can basically be rationalized in the same way. The models introduced
independently by Verheyen and by Egré are meant to support the idea
that vagueness is fundamentally a semantic phenomenon, that is,
speakers can vary faultlessly in positioning their thresholds for
categorization differently along the same latent dimensions. Arguably,
however, the idea of a fixed threshold within each speaker may appear
to cohere better with an epistemicist view of the meaning of vague
terms, that is with the idea that vague expressions fundamentally
denote crisp properties. In this paper we extend the threshold model
proposed in Egré (2017) to combine it with the idea that thesholds
themselves could be probabilistic. The model incorporates the two
levels of uncertainty distinguished by Barker (2002) and by Lassiter
(2011), but prima facie, this time it is free of any remaining
epistemicist commitment. We discuss two difficulties for that
approach: the first is to show that those two levels are effectively
needed to model vague judgments. The second is how to interpret such
moving thresholds within an individual for the same category. Several
options can be considered: the fluctuation could be due to the same
individual changing criteria of application over time; or to the
individual being uncertain about specific contextual properties; or to
the individual sampling over plausible collective values but being
uncertain about any single value. We discuss those various assumptions
and outline ways to tease apart those hypotheses.


For inquiries, please contact Peter Hawke (, Aybüke Özgün (, or Tom Schoonen (